CARTILAGE AND BONE TISSUE
Dr. Crissman
H.I.R Chapter 7
CARTILAGE
Cartilage is one form of connective tissue that accentuates the intercellular
(extracellular) matrix. As with most connective tissues, the cartilage matrix is
produced
and
maintained
by fixed
cells which
are
known
as chondroblasts and chondrocytes, respectively. All cartilage is characterized
by
large
round
cells
surrounded
by
large
amounts
of
amorphous extracellularmatrix. The predominant extracellular fiber determines
the specific type of cartilage. Because of the nature of the constituent
components of the ground substance and the embedded fibers, the matrix is
"strong" but somewhat deformable. Hyaline cartilage normally is found in the
trachea, costal cartilage of ribs, developing long bones of fetus,
and articular cartilage
of
the synovial joints
where
flexibility, compressiblity and slipperiness is needed. .
HYALINE CARTILAGE
[MCO 0060] Trachea & Esophagus, Rodent Java HIR-frame 358-362
[MCW 021] Trachea, H&E Java
[SL 035] Trachea Java
Hyaline cartilage forms an incomplete red staining ring (MCO 0060, blue
staining in the other two slides) within the wall of the round trachea. The holes
or openings within the cartilage ring are the lacunae (lakes)
containing chondrocytes. The chondrocytes are shrunken during processing and
are seen as dark masses in the center of the open lacunae.The red (blue)
staining material between the lacunae is the cartilage matrix. This
contains collagenous fibrils which are masked by hyaline ground substance.
The capsule is the more basophilic staining matrix recently laid down adjacent
to the chondrocytes. It is basophilic due to its higher concentrations
of chondroitin sulfates. The interterritorial matrix is the lighter-staining matrix
farther away, between the cartilage cells. The difference in staining properties
is usually only seen in cartilage that is still growing and not in that which is
being maintained (in the mature or adult human). The perichondrium is the
layer of flattened connective tissue cells which encloses the cartilage. It has an
outer, fibrous layerand an inner, chondrogenic layer. The cells of
the chondrogenic layer are more rounded instead of flattened as in the fibrous
layer. The perichondrium is separated from the cartilage by shrinkage artifact.
[MCO 0017] Fetal Finger, Early Endochond. Ossif. Java
HIR-frames 398-399, 362, 405-408
[MCO 0617] Fetal Finger, Later Endochond. Ossif. Java
[LH 0026] Fetal Finger Java
[SL 004] Fetal Digit (Endochondrol Oss.) Java
In these slides, hyaline cartilage serves as a template for long bone
formation. The light blue staining tissue is the hyaline cartilage precursor
model of the phalanges. Use this slide to distinguish between appositional
growth and interstitial growth of cartilage. Interstitial growth is represented
by isogenous groups ("cell nest") of chondroblasts. These cell nests consist of
groups of chondroblasts(2,4 or 8 cells) closely clustered together deep within
the mass of cartilage. These cells are the progeny of a
single chondroblast. Appositional growth occurs at the edge of the cartilage
mass by mitosis in the chondrogenic layer of the perichondrium. This can be
recognized by the larger, rounder cells immediately subjacent to the fibrous
(flattened fibroblasts) layer of the perichondrium. The hyaline cartilage model
of long bones permits the fetus to bend and flex more easily during the birth
process.
In most of these slides, a forming synovial joint is also being formed. Look for
the
clear synovial cavity
between
the
cartilage
shapes,
the
forming articular surfaces lackingperichondrium, and the forming connective
tissue capsule which closes the cavity between the two cartilage models of long
bone. What are the five structural characteristics of anysynovial joint?
ELASTIC CARTILAGE
[MCO 0012] Elastic Cartilage, Epiglottis Java HIR-frames 365-367
[SL 065] Epiglottis (Elastic Cartilage) Java
This long organ has a broad base at one end and tapers to a point at the other
end. Running down the middle from one end to the other is a darkly stained rod
of elastic cartilage.Elastic cartilage is similar to hyaline cartilage with elastic
fibers in the matrix. The chondrocytes lie within the diagnostic large ovalshaped lacunae (clear). The matrix between the cells is quite dark due to masses
of darkly stained elastic fibers. The VIH stain is specific for the elastic fibers
and stains them black. In H & E stained elastic cartilage, the elastic fibers are
quite difficult to visualize. The stretch and rebound characteristic of the elastic
fibers allows the organ containing elastic cartilage to spring back to its original
shape and position. This is what occurs in the epiglottis, external pina of the ear
and auditory tubes.
FIBROCARTILAGE
[SL 093] Intervertebral Disc Java HIR-frames 368, 369
[LH 0020] Symphysis Pubis Java
Fibrocartilage appears like dense connective tissue with cartilage cells. There
are large round chondrocytes embedded in a matrix full of large bundles
of collagenous fibers. The ground substance is greatly reduced due to the great
numbers of collagen fibers present. It is found where cartilage is subject to
pressure, such as in the intervertebral discs (SL 093) between the vertebrae,
pubic symphysis or where tendons or ligaments attach to bone. This section
comes
from
the intervertebral disc
between
two
vertebrae.
Thechondrocytes retain their characteristic oval or round shape to distinguish it
from dense irregular or regular connective tissue. This cartilage tissue
is avascular like the other two types of cartilage. The slightly pinker staining
material at the edges is bone tissue from the adjacent vertebrae. Be sure to see
the demonstration of the developing fetal vertebrae and intervertebral disc.
The fibrocartilage is located between the two coxal bones of the pelvis in the
pubic symphysis (LH 0020). The darker staining marrow marks the bones and
the pinker stainedfibrocartilage has the characteristic tightly packed, wavy,
bundles of collagen fibers with large round cells present. Be able to describe
the structural characteristics of each type of cartilage.
BONE
There are 5 types of cells in bone tissue: (1) osteoblasts, which form the bone
tissue; (2) osteocytes which maintain the bone as they lie within lacunae in the
bone substance, and (3)osteoclasts which resorb bone; (4) bone lining cells that
separate the bone tissue from the rest of the body and
(5) osteoprogenitor cells which can not be readily identified. Bone is a vascular
and dynamic tissue which undergoes constant remodeling through
continuous resorption and formation of bone tissue. Osteocytes and bone tissue
are periodically removed by the remodeling process. Osteocytes have processes
which extend to the perivascular space to bring in nutrients. The external
surface of bone tissue is covered by periosteum which acts and looks similar to
cartilage's perichondrium. The periosteum has two layers, an outer fibrous
layer and an inner osteogenic layer. There are Sharpey's fibers or perforating
fibers, which are bundles of collagen fibers that enter the bone matrix from
the periosteum. The internal surface of bone tissue is covered by a single-cellthick layer called the endosteum.
The bone matrix is composed of an organic and an inorganic
component. Collagen makes up 90% of the organic component of bone which
accounts for approximately 30 - 40% of bone substance. The other 60 - 75% of
bone is inorganic in nature and is predominantly calcium phosphate and
carbonate in the form of hydroxyapatite crystals positioned between the
collagen
fibers. This
combination
of
collagen
fibers
and
the hydroxyapatite crystals is like using straw in clay to make bricks. This gives
bone great strength with resistance to breakage or deformation. Because of the
presence of the inorganic component, bone tissue contains only a small amount
of ground substance.
Bones, like a femur, are grossly divided into compact (dense)
and spongy (trabecular) bone. Compact bone forms the very dense outer walls
(cortex or cortical bone) of the shafts in long bones.
Spongy bone is made of a fine meshwork of spicules of bone
called trabeculae. Spongy bone is found inside the shafts of bones. The space
between the spicules is filled with bone marrow.
Compact bone is vascularized via Haversian systems (Osteons). Nutrient
vessels enter from the external aspect of the bone via the periosteum, pass into
the bone and give off vessels which run the length of
the Haversian system. Volkmann's canals are diagonally-oriented channels
containing blood vessels which supply the Haversian canals. The Volkmann's
canals do not have layers of concentric lamellae of bone which is characteristic
of the Haversian systems.
The Haversian system, (osteon) the basic structural and functional unit of
compact bone, consists of the (1) Haversian canal which contains blood vessels
and nerves, and (2) concentric lamellae of collagen fibers. In cross section,
these lamellae appear as concentric rings around the Haversian canal. These
lamellae of collagen can only be seen in polarized light.Lacunae, which
contain the osteocytes, are also arranged concentrically around
the Haversian canal within the lamellae.
[MCO 0014] Compact bone, Dry Java HIR-frame 376
[SL 002] Bone (Ground) Java
[UW 2015] Bone (Ground) Java
These slides are both cross and longitudinal sections of ground bone. They are
prepared by grinding down a thin piece of dried bone until it can be viewed
under the microscope.The Haversian systems can be clearly seen in this type of
preparation. The spaces of the ground bone (Haversian and Volkmann canals,
lacunae, and canaliculi) are dark due to being filled with Indian ink (or clear
where the ink did not penetrate).
In cross section, the large dark spaces are the Haversian Canals (central)
containing
blood
vessels
at
the
center
of
the Haversian System. Osteocytes occupy the dark lentiformlacunae arranged
in several concentric rings around the central canal. Lamellae of collagen fibers
are layered in between the rings of osteocytes, but they can not be seen in these
sections without polarized light. Canaliculi are thin dark threads running from
the lacunae of one ring to the lacunae of adjacent ring of cells.
The canaliculi are the fine tunnels containing the osteocyte cell processes
which communicate with adjacent cells. In the longitudinal
section, Haversian systems usually are 3-5mm in length. Numerous osteons are
packed end-to-end and side-to-side to form the compact bone.
Cement lines are refractile lines (light) at the outermost extent of
individual osteons. The cement line has very few collagen fibers in it but it is
still highly calcified. The interstitial lamellae, which are remnants of
former osteons, are seen as incomplete parts of Haversian systems between the
complete Haversian systems. The layering of lacunae is still seen, but there is
no central canal with which these layers are associated. Volkmann's canals are
typically vessels within tunnels running perpendicularly to the bone surface.
They are characterized by the lack of concentric rings of osteocytes around the
vessel.
Make sure to look for the same structures in the longitudinal section.
[MCO 0018] Compact Bone, Decalcified Java HIR-frame 373
[UW2016] Decalcified Bone & Marrow Java
[UW 2020] Calvaria, Monkey Java
In the cross section of decalcified bone, look to visualize the cellular and
organic elements of bone. Look for the fibrous and osteogenic layers of
the periosteum. In some slide, theperiosteum is artifactually separated from the
dense cortical bone. Sharpey's fibers are not readily visible in these slides, see
demonstration. The endosteum is represented by a single layer of thin flat
nuclei on the surface of the marrow cavity. You have to look carefully to
separate them from the round hemopoietic cells of the red bone marrow. In the
compact bone, identify the osteocytes and their cell process in
the canaliculi. Osteons can be seen in UW 2020. In MCO 0018, look for
the outer circumferential lamellae adjacent to the periosteum. A thinner layer
of inner circumferential lamellae can be seen adjacent to the endosteum. These
lamellae
are
formed
from
the periosteum and endosteum,
respectively. Osteons are the basic functional unit of dense bone
tissue. Trabecular packets are the functional unit in the structure of trabecula in
spongy bone. The larger trabeculamay also have osteons present. Make sure to
look for the same structures in the longitudinal section.
LOOK FOR
DEMONSTRATION
OF TRABECULAR
PACKETS & SHARPEY'S FIBERS.